(1) Field of Invention
The present invention relates to ground terminals or antennas that receive and send communication signals to geo-stationary satellites and, more particularly, to ground terminals with rejection capabilities for satellites in orbits that are close enough to the orbit of a desired satellite so as to cause interference.
(2) Description of Related Art
Satellite communication became possible in 1957 when Russia launched Sputnik, the first man-made satellite. The first active direct-link communications satellite, Telstar, a joint project of AT&T, Bell Labs, NASA, the British General Post Office, and the French National PTT (Post Office) was launched in 1962. The first geo-stationary satellite placed in orbit was Syncom 3, launched on Aug. 19, 1964. A satellite in a geostationary orbit appears to be in a fixed position to an Earth-based observer. A geostationary satellite revolves around the Earth at a constant speed once per day over the equator and is considered to be in a geo-synchronous orbit. The orbiting satellites so situated are considered to be part of the geo-satellite belt and for consistency are referred to herein as geo-satellites.
Satellites in the geo-stationary orbit are particularly appealing because from the perspective of a viewer, the satellite appears to be stationary. This popularity has resulted in a glut of satellites vying for an ever decreasing number of available slots in the arc of the geo-stationary orbit. As the geo-stationary orbit becomes more crowded, the need for an antenna system that can discern the signal from a desired satellite to the exclusion of those in nearby orbital slots is becoming increasingly acute. Fulfilling this need without requiring extensive and expensive large reflectors and fine-tuning in aiming is an important goal.
Through voluntary national and international agreements, geo-satellites are spaced a few degrees apart in geostationary orbits to assure minimal interference between satellites in close orbital proximity. However, as the demand from business, consumers, and governments increases, satellites are allocated over the close-by slots servicing different coverage areas for both C and Ku band applications. Coordination between service providers with satellites in nearby orbital slots, which service satellites in closely-spaced coverage areas using the same spectrum, is a technological challenge because of interference between the signals of the satellites in close directional proximity to each other. There are solutions to resolve these interference issues using both space-based and ground-based approaches.